1. Technical Field of the Invention
The present invention relates to an apparatus and method for detecting scattered material such as powder or foam contained in an envelope, a capsule, a container or the like by use of terahertz waves without unsealing the envelope or the like.
2. Description of the Related Art
Hereinafter, electromagnetic waves having frequencies around 1 THz, that is, far-infrared rays and sub-millimeter waves in this frequency region will be called “terahertz waves”. The terahertz wave is positioned in a boundary between a light wave and a radio wave, and has characteristics of both of the light and radio waves.
One of the characteristics of the terahertz wave is that it is the shortest wavelength band having material transmitting properties of the radio wave as well as the longest wavelength having straight moving properties of the light wave. More specifically, the terahertz wave is similar to the radio wave in that the wave can pass through various materials. Since the terahertz wave has a short wavelength (around 1 millimeter to 30 micron meters), the wave can obtain the highest spatial resolution in a radio wave band. The terahertz wave is similar to the light wave in that the wave can be treated by lens or mirrors.
Apparatuses utilizing the characteristics of the terahertz waves are described, for example, in Patent Documents 1, 2 and the like.
In “Apparatus and Method for measuring Physical Properties of Powder by means of Terahertz Electromagnetic Wave” of Patent Document 1, as shown in FIG. 1, the apparatus comprises: means 51 for holding powder; irradiation means 52a, 52b, 52c for irradiating the powder with terahertz electromagnetic waves; receiving means 53a, 53b, 53c for receiving the terahertz electromagnetic waves which have passed through the powder to convert the waves into electric signals; means 54 for acquiring from outputs of the receiving means a difference of propagation times or amplitudes between positions of the powder where the terahertz electromagnetic waves pass; and image processing means 55 for processing an image to display the characteristics of the powder in a display based on the difference. The apparatus measures the characteristics of the powder.
In an aspect, a transmittance, a refractive index, a filling ratio and the like of the powder are measured by this means.
In “Method and Apparatus for Differential Imaging using Terahertz Wave” of Patent Document 2, as shown in FIG. 2, terahertz waves 64a, 64b on two different wavelengths are generated in a frequency range of about 0.5 to 3 THz, a material 65 to be inspected is irradiated with the terahertz waves on two wavelengths 64a, 64b to measure the transmittances, and presence of a target having dependence of the wavelength on absorption of the terahertz wave is detected from a difference between the transmittances.
In the aspect, the dependence of DNA of salmon or the like on the wavelength is measured by this means.
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2004-61455 titled “Apparatus and Method for measuring Physical Properties of Powder by means of Terahertz Electromagnetic Wave”
[Patent Document 2]
Japanese Patent Application Laid-Open No. 2004-108905 titled “Method and Apparatus for Differential Imaging using Terahertz Wave”
In recent years, one kind of terrorist act has been a social problem in which anthrax bacteria or chemicals are distributed by mail. Conventional X-ray photographs allow shapes of these contents to be determined, but do not allow their properties to be determined unless containers are unsealed. Therefore, for example, when powered chemicals are mailed in an envelope, they cannot be detected unless the envelope is unsealed.
Moreover, even in inspection of products such as medicines, it cannot be detected from the outside whether or not the products are contained in a capsule or a container, unless the capsule or the container is unsealed.
Furthermore, even in a case where foam and the like exist as defects in opaque plastic products, ceramic products, paint, petroleum, glaze, magnetic paint and the like, the defects cannot be heretofore detected from the outside in a non-destructive manner.